A typical hand-operated grease gun includes a cylindrical reservoir from which grease is exuded into a hand-operated, piston-type pump disposed in a housing closing one end of the reservoir. The grease is expelled from the pump under pressure through an outlet in the gun end housing into and through a removable output tube, which tube may be rigid or flexible and of varying length with an appropriate nozzle at its outer end. Unfortunately, grease guns of this type are beset with the problem of air pockets. Air may be trapped between the grease and the pump when the gun is initially filled, or poCkets of air may be trapped within the grease itself. This is true even when the grease is supplied in paperboard cylinders for insertion into the gun, as well as when it is simply filled from a remote source of bulk grease. Once the trapped air gets into the pump it renders the pump useless insofar as its ability to expel grease from the nozzle is concerned. That condition continues until the air is finally exhausted from the nozzle by repeated strokes of the pump which by repeated compressions of the air gradually moves the latter through the output tube.
All users of these guns are well aware of this problem and the angry frustration it generates. One is lubricating, say, a piece of machinery, stroking the pump's operating lever, when suddenly the lever goes "limp", signaling that an air pocket has reached the pump. The job is thus interrupted until the air can be expelled. The longer the output tube, in order to reach otherwise inaccessible lubrication points, for instance, the greater the time it takes to expel the air and the greater the frustration it engenders. Such longer output tubes, or extensions, are often used to lubricate construction equipment and farm machinery, frequently under less than ideal conditions and often when downtime for service is at a premium. It is believed that in such extensions the air expands and contracts similarly to air in a cylinder of an air-type spring, maintaining sufficient back pressure seepage to make it most difficult for the pump to regain its primed condition.
The prior art has recognized the above problem in the form of a valve assembly to be mounted between the pump assembly of the grease gun and the dispensing extension. The valve assembly is in essence a bleeder-type push valve which communicates via a "T"-fitting with the outlet duct of the pump leading into the dispensing extension. The prior art valve features a stem disposed in the vertical leg of the "T"-fitting, the stem normally being biased outwardly from the outlet duct with its lower portion against a seat into a closed position. The lower portion of the stem features a sealing ring, such that when pressure is built up in the outlet duct, the valve remains normally sealed shut to air and grease. The angular disposition of the valve stem with respect to the pump and handle assembly of the grease gun depends, of course, on tolerances and thread positions on both the fittings on the grease gun and the "T"-fitting housing the valve. As a result in general, the valves will not be oriented in definite, readily accessible positions with respect to the handles of grease guns, when the "T" -fittings are securely seated at the outlet duct of the grease gun.
In view of the known prior art, a need still exists for a simple but effective and readily accessible attachment for grease guns, particularly hand-operated grease guns, to allow trapped air pockets to be removed from a point immediately downstream of the pump. It is, consequently, an object of the invention to provide such an attachment, and particularly one which is accessible regardless of the degree to which threads need to be engaged for proper seating and which shows such other advantages as will become apparent from the specification.